Formable alloys for use in manufacturing highly shaped cans and bottles are desired. For shaped bottles, the manufacturing process typically involves first producing a cylinder using a drawing and wall ironing (DWI) process. The resulting cylinder is then formed into a bottle shape using, for example, a sequence of full-body necking steps, blow molding, or other mechanical shaping, or a combination of these processes. The demands on any alloy used in such a process or combination of processes are complex. Thus, there is a need for alloys capable of sustaining high levels of deformation during mechanical shaping and/or blow molding for the bottle shaping process and that function well in the DWI process used to make the starting cylindrical preform. In addition, methods are needed for making preforms from the alloy at high speeds and levels of runnability, such as that demonstrated by the current can body alloy AA3104. AA3104 contains a high volume fraction of coarse intermetallic particles formed during casting and modified during homogenization and rolling. These particles play a major role in die cleaning during the DWI process, helping to remove any aluminum or aluminum oxide build-up on the dies, which improves both the metal surface appearance and also the runnability of the sheet.
The other requirements of the alloy are that it must be possible to produce a bottle which meets the targets for mechanical performance (e.g., column strength, rigidity, and a minimum bottom dome reversal pressure in the final shaped product) with lower weight than the current generation of aluminum bottles. The only way to achieve lower weight without significant modification of the design is to reduce the wall thickness of the bottle. This makes meeting the mechanical performance requirement even more challenging.
A final requirement is the ability to form the bottles at a high speed. In order to achieve a high throughput (e.g., 500-600 bottles per minute) in commercial production, the shaping of the bottle must be completed in a very short time. Thus, the materials will be deformed employing a very high strain rate. While aluminum alloys in general are not known to be strain rate sensitive at room temperature, the high temperature formability decreases significantly with increasing strain rate, particularly for Mg-containing alloys. As known to those of skill in the art, the increase in fracture elongation associated with increases in forming temperature in a low strain rate regime diminishes progressively with increasing strain rate.